The long term goal of this study is to determine how estrogen stimulates growth of the mammalian uterus. Estrogen stimulates hypertrophy and hyperplasia of the uterus and other organs of the female genital tract. This effect is mediated directly at the target tissue via interaction of estrogen with its specific receptor. It is believed that many of estrogen's effects are mediated by growth regulatory factors whose synthesis and/or activity are regulated by estrogen. Despite the significance of these processes to human fertility, relatively little is known about the nature of these factors. In this study, the powerful, sensitive method of reverse transcription-polymerase chain reaction (RT-PCR) will be used to evaluate estrogen's effects on the expression of growth regulatory factors in the rat uterus. In part 1 (Specific Aim I), the ability of estrogen to control the expression of four growth factors that seem likely to play important roles in the cyclic development of the uterus, but whose expression in the uterus is almost completely unexplored, will be determined. These include: 1) acidic fibroblast growth factor (FGF), 2) basic FGF, 3) keratinocyte growth factor (KGF), and 4) vascular endothelial growth factor (VEGF). The FGF's are broad spectrum mitogens that stimulate proliferation of a wide range of cells and are thought to be involved in neovascularization. Expression of basic FGF by human endometrial adenocarcinoma cells has been shown to be stimulated by estrogen. KGF is similar in structure to the FGF's but is specific for epithelial cells; KGF is thought to be a stromally-derived regulator of epithelial cell proliferation. It could, therefore, play a role in the proliferation of endometrial epithelium. VEGF is similar in structure to platelet derived growth factor (PDGF). It is a potent, specific endothelial cell mitogen; in addition it increases vascular permeability. VEGF could play a role in the development and functioning of the uterine vasculature. RNA will be extracted from uteri of control and estrogen-treated immature rats at various intervals after treatment and the expression of the mRNA's for these factors quantitatively analyzed. In part 2 (Specific Aim 2), the induction of as yet undefined mRNA's by estrogen in the uterus will be examined. This will be done using the method of subtraction hybridization followed by PCR amplification of the subtracted mRNA's. To do this, a defined DNA adaptor is ligated to both ends of the products a cDNA synthesis reaction performed on the subtracted mRNA's followed by standard PCR amplification, sequencing of the amplified products, and comparison of the sequences to known genes. In this way, low abundance mRNA's induced by estrogen may be identified; most growth factor mRNA's are relatively rare. These studies will provide new insight into the nature of the growth regulating factors involved in sex steroid hormone action on the female genital tract.